Apparatus for measuring, and indicating, the thickness of a non-metallic coating on an arcuate metal surface

Apparatus for measuring, and indicating, the thickness of a non-metallic coating on an arcuate metal surface, comprising:

• at least one measuring head for positioning relative to said coating;
• at least one support member on each measuring head for supporting said measuring head relative to said coating;
• a sensing member on each measuring head and arranged to develop a signal representative of the distance between said sensing member and said arcuate metal surface;
• a profiled surface on said support member for presentation to said coating, said profiled surface having a Vee shape with convex arcuate sides when viewed in a direction parallel to the axis of the arcuate metal surface, the arcuate sides initially defined by sequentially positioning a series of metal cylindrical mandrels of different diameters relative to the sensing member with the axes of the mandrels lying in a common plane normal to the sensing member, so as to develop a signal of the same magnitude from the sensing member for each mandrel, each arcuate side being a curve which is tangential to the peripheries of the mandrels at these respective positions, the penetration of said arcuate metal surface and coating into said Vee shape varying with the outer diameter of the coating to offset variations in the signal resulting from variations in the outer diameter of the non-metallic coating;
• signal processing means connected to said sensing member, for processing said signal from said sensing member;
• means connected to said signal processing means for displaying an output therefrom, said output indicative of the thickness of said non-metallic coating.